Treatment of butane



Patented July 2?, 19

TREATMENT OF BUTANE Vladimir N. Ipatiefl' and Herman Pines, Chicago,

Ill., assignors to Universal Oil Products Company, Chicago, 111., a corporation of Delaware No Drawing. Application March 11, 1940,

Serial N0. 323,386

1 Claim." (01. 260-4835) This application is a continuation-in-part of our co-pending application Serial No. 103,383, filed September 30, 1936, now Patent No. 2,283,142, granted May 12, 1942.

This invention relates more particularly to the treatment of butane of normal or straight-chain 7 structure.

In a more specific sense the invention is concerned with a process whereby normal butane is converted into isobutane, the process involving the use of special catalysts and particular conditions of operation which favor the isomerization reactions so that relatively high yields of the iso-compcund are produced.

Since the invention is concerned principally with the two 4-carbon atom paraffin hydrocarbons and their transformation, one into the other, the following table is introduced to indicate the structure and the principal physical characteristics of these two compounds:

Properties of butanes Butanes are-produced in considerable quantities in the oil refining industry. They occur in substantial amounts in natural gases (in which the normal compound usually predominates), in refinery gases which are evolved from crude petroleum storage tanks, and in the primary distillation of crudes, and they are also present in considerablepercentages in the gases produced incidental to cracking heavy petroleum fractions for the production of gasoline. In the case of cracked gas mixtures the relative proportions of iso and normal butane vary, but the ratio of the iso to the normal compound is as a rule considerably higher than in natural gas.

Butanes may be considered as more or less marginal compounds in respect to their desirability in ordinary gasoline, that is, a certain percentage of them is essential for suficient vapor pressure to insure ease in starting, while an excess tends to produce vapor look. For these reasons the total percentage of -carbon atom hydrocarbons is commonly adjusted in conjunction with the boiling range and vapor pressure of the other gasoline components to produce a gasoline of desirable starting characteristics according to seasonal demands.

The butanes at the present time bear a further important relationship to oil refining in that their excess production is being utilized as a source of gasoline either by ordinary thermal cracking or by special catalytic dehydrogenation processes followed by polymerization in which catalysts may or may not be used. Investigations have shown that isobutane is considerably more amenable to cracking and dehydrogenation, both with and without catalysts, than the normal compound. Considering the corresponding mono-' olefins, the normal butenes are considerably more dimcult to polymerize, either thermally or catalytioally, than isobutene, and it is found also that the octenes representing thedimers of isobutene are of higher antiknock value than those from normal butenes, which holds also for the octanes produced by hydrogenation. It is, therefore, of considerable importance at the present time to convert as much as possible of the normal butane production into isobutane, and the present invention is especially concerned with a process for accomplishing this object.

In one specific embodiment the present invention comprises the treatment of normal butane or hydrocarbon mixtures containing substantial percentages thereof with catalysts comprising boron trifiuoride and hydrogen fluoride to efiect isomerization reactions.

Boron trifluoride (BFa) is normally a colorless gas, having a. boiling point of 101 C. and a melting point of l20 C. so that it is most readily handled for catalytic work in a vaporous condition. Hydrogen fluoride has a boiling point of +20 Grand therefore the proposed catalytic mixture of compounds is readily employed in vapor phase reactions or for the treatment of hydrocarbons in liquid phase under selected temperature and pressure conditions. In accordance with the present invention, it has been found that various proportioned mixtures of boron trifluoride and hydrogen fluoride have a catalytic eifect in isomerizing normal butane to produce isobutane where this catalytic property is not exhibited by either of the compounds separately so that there is obviously a joint promoting action although it is recognized that the idea of promoter catalysis is not entirely understood and the term is sometimes abused. As a rule the amount of boron trifiuoride is in excess of the hydrogen fluoride in the most efllcient mixtures, but this is not to be taken as an invariable rule fluoride, and normal as widely diflerent effects may be obtained by varying the proportions of the two catalytic components of the preferred mixtures.

The temperature, pressure, and time of contact necessary for eflecting an optimum amount of isomerization will, in the case oi butane-containing mixtures, vary with the composition of said mixtures so that only broad ranges can be given for these operating conditions. In general, temperatures from ordinary atmospheric to approximately 300 C., normal atmospheric or erately superatmospheric pressures, and varying times of contact may be employed depending upon whether the operations are conducted in batch or continuous types or plants. In any case there will be an optimum set of conditions at which maximum. isomerization may be effected with minimum decomposition involving the breaking of carbon-to-carbon bonds and the formation of hydrocarbons of lowerv and higher molecular weights than the original butane treated.

The process may be operated under batch or continuous conditions. Batch operations may be conducted by adding boron fluoride, hydrogen butane to a closed pressure reactor, after which the reactor may be agitated or the contents stirred mechanically .while the temperature and pressure are raised by the application of external heat to produce a temperature corresponding-to the maximum production of isobutane. ried out in liquid or vapor phase by controloi temperature and pressure employed. Batch type operation is adapted better-to small scale production, and plants of considerable capacity are generally operated best in a continuous manner;

If desired, pressure of, an addedgas such as hy-' drogen, methane, etc.,- may be-applied to assist in maintaining the reaction mixture in s'ubstantlally liquid phase. 1

In continuous isomerization operations, normal butane or thehydrocarbon traction, containing normal butane may bepumped through a heater at a temperature and pressure'withinthe ap-" proximate ranges hereinabove specified and reaction may be brought about along the line of flow by the separate or joint introduction of proportioned amounts of-boron trifluoride and hydrogen fluoride and by maintaining the mixture at the desired reaction temperature for a suitable time to effect the desired isomerization. In the absence of moisture, corrosion ot'equipment will be relatively low when using these substances. After passage through the heater, the reactants may be conducted toan insulated reactor for the completion of the desired isomerization after mod- This type of operation may be car-- which the constituents may be separated readily by fractional distillation and the boron fluoride and hydrogen fluoride which have not been cons'umed by reaction with the hydrocarbons may be recycled to further isomerizing use. The mixture resulting from isomerization treatment may be iractionally distilled to separate the desired isobutane, unconverted normal butane which may be recycled to further isomerization treatment, and relatively small amounts of organic fluorine compounds. Where the time factor is not too long, butane isomerization may be made continuous by passing this hydrocarbon or butane-containing mixture and the catalysts through baffled tubular treaters of suitable length to insure the proper time of contact.

The following example is introduced for the purpose of illustrating the type of results obtainable by the use of the process of the invention, although not with the intention of unduly limiting its generally broad scope. V

Eighty-four parts by weight of normal butane was placed in a rotatable pressure vessel and a mixture of 1'7 parts by weight of boron trifluoride and 13 parts by weight of hydrogen fluoride was introduced. The vessel was closed and the contents agitated by rotating the vessel at 150 C. under a pressure of approximately 20 atmospheres.

The products of the reaction after recovery of substantially unchanged boron fluoride and hydrogen fluoride were as follows:

Thus with recycling of unconverted n-butane, an ultimate yield of approximately isobutane may be obtained.

The character of the present invention and its value are evident from the foregoing specification and example introduced, although neither section is intended to unduly limit its generally broad scope.

We claim as our invention:

A process for producing isobutane which comprises subjecting normal butane to the action of boron fluoride under conditions and in the presence of .an amount of hydrogen fluoride such that isomerization of normal butane constitutes the principal reaction in the process.

I VLADIMIR. N. IPATIEFF.

HERMAN PINES. 

